Little is known how the brain compensates for the body's own movements and how it deals with the sensory reafference generated by such movements. What is known indicates not a single solution, but several. The experiments proposed will study this problem in a specially favorable case, the electrosensory system in catfish. Electroreception is the sensory capability of certain vertebrate taxa to detect and orient to weak electric fields. The experiments described in this proposal constitute an investigation of sensory processing in the electrosensory system of the catfish, Ictalurus punctatus. Experimental neuroanatomical and neurophysiological methods will be employed to examine neural processes in the primary electrosensory nucleus of the medulla. Specifically examined will be the central anatomical organization of primary afferent nerve fiber terminals as well as that of afferent fibers originating from central neurons, particularly the commissural interconnections between the bilateral medullary electrosensory nuclei. Electrophysiological methods will be employed to determine the functional role of these pathways in electrosensory processing in the medulla. I will investigate (1) possible lateral interactions among electrosensory neurons within the nucleus (2) the role of the commissural pathway in reducing electrosensory reafference and (3) the role of descending afferent fibers originating in cerebellar and midbrain nuclei. Both of these possible mechanisms are directly related to the central problem of reducing self-generated sensory interference in central sensory processing. In addition to providing fundamental data concerning medullary sensory processes, this study will also provide important comparative data. Electroreception is a primitive vertebrate character that has been 're-evolved" by catfish. Comparisons with primitive electrosensory systems will yield information concerning the evolution of sensory systems in the vertebrate brain.